Resiliently-mounted blast-shield for the tank of an oil-circuit breaker

ABSTRACT

The invention teaches the use of a shock-resisting non-gasabsorptive plate of insulating material mounted on the internal tank walls of an oil circuit-breaker, and centered on the current-interrupter vents. Resilient rubber insulators are used in resiliently mounting the shock-resisting plate to absorb the shock forces exerted by the ionized gas products striking the shield. The insulating barrier is permitted to resiliently move to accommodate short-duration pressure differences on the front and rear faces thereof, thus avoiding damaging deflections of the plate.

United States Patent [1 1 [111 3,805,002 Hess et a]. Apr. 16, 1974 [54] RESILIENTLY-MOUNTED BLAST-SHIELD 2,998,499 8/1961 Mankoff et al. ZOO/150 R FOR THE TANK OF AN OIL-CIRCUIT BREAKER [75] Inventors: Robert L. Hess, North Versailles;

Edward P. Donohue, Pittsburgh, both of Pa.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Dec. 15, 1971 [21] Appl. N0.: 208,482

[52] [1.8. CI 200/150 R [51] Int. Cl. H0lh 33/68 [58] Field of Search 200/150 R [56] References Cited UNITED STATES PATENTS 2,734,973 2/1956 MacNeill et al. ZOO/150 R Primary Examiner-Robert S. Macon Attorney, Agent, or FirmW. R. Crout [5 7] ABSTRACT The invention teaches the use of a shock-resisting non-gas-absorptive plate of insulating material mounted on the internal tank walls of an oil circuitbreaker, and centered on the current-interrupter vents. Resilient rubber insulators are used in resiliently mounting the shock-resisting plate to absorb the shock forces exerted by the ionized gas products striking the shield. Theinsulating barrier is permitted to resiliently move to accommodate short-duration pressure differences on the front and rear faces thereof, thus avoiding damaging deflections of the plate.

9 Claims, 8 Drawing Figures PATENIEHAPH i6 .974

sum 2 or 3 FIG. 3

RESILIENTLY-MOUNTED BLAST-SHIELD FOR THE TANK OF AN OIL-CIRCUIT BREAKER CROSS-REFERENCES TO RELATED APPLICATIONS Applicants are not aware of any related applications pertinent to the present invention.

BACKGROUND OF THE INVENTION Some designs of circuit-breakers and oil breakers, in particular, vent a large volume of ionized gas and are products during the interruption of an electrical current. Normally, the ionized gas is expelled out of the current interrupter and toward the grounded tank wall. When a high current is interrupted, with a relatively long arcing time, the volume and pressure of ionized gas, developed and vented toward the inner tank wall, can, on occasion, cause failure of the electrical insulation strength. The installation of a resilient blast-shield in an oil circuit-breaker prevents the vented gaseous products from striking the tank wall, and maintains a protected layer of insulating oil. This permits an increase in the dynamic insulation-withstand strength of the oil circuit-breaker. Previous attempts to measure this dynamic insulation strength have been limited by the inability of testing facilities to supply the simultaneous combination of high-voltage and high currents required for testing high-voltage oil circuit-breakers. One of the hazards, during the high-voltage testing of oil circuit-breakers, such as those of the 345 KV type, is the possibility of internal voltage breakdown during interruption of large currents. An internal voltage breakdown in a circuit-breaker, while in service in an electrical utility system, could be calamitous.

SUMMARY OF THE INVENTION According tothe present invention; the solution to the foregoing serious problem comprises the resiliently mounting of an insulating plate, say of glass-reinforced polyester laminate, for example, on oil-resistant, resilient rubber, or elastomeric spacers, spaced, for example, four inches from the inner tank wall, and centered on the interrupter vents. This resilient blast-shield provides a cushion for the vented gaseous are products formed during current interruption, and prevents the gas from striking the grounded tank wall. The end result is to permit a higher dynamic insulation-withstand strength to be obtained. The invention is particularly suitable for high-voltage oil circuit-breakers, such as those rated 345 KV, 25,000 M.V.A., which use, for ex ample, four of these blast-shields for each oil tank.

Accordingly, a general object of the present invention is to provide an improved resiliently-mounted blast-shield construction for oil-type circuitinterrupters which will resist the shock forces encountered during interruption, and will provide a cushion of clean uncontaminated oil behind the blast plates, so as to maintain entact the internal dielectric strength of the tank wall.

An additional object of the present invention is the provision of an improved blast-shield construction for oil-type circuit interrupters, which is resiliently mounted, and is capable of absorbing the tremendous lateral forces encountered during interruption of highfault currents by the breaker.

Still a further object of the present invention is the provision of an improved economical and easily installed blast-shield construction for an oil-type circuit interrupter, which is resiliently mounted, and serves to cushion the lateral gas shock forces encountered during high-fault circuit interruption.

Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional fragmentary view taken through a high-voltage oil circuit-interrupter, illustrating an application of the present invention, in which two resiliently-mounted blast-shields are applied on opposite sides of one of the two interrupting assemblages disposed in the tank;

FIG. 2 is a considerably-enlarged detail view taken along the lines lIlI of FIG. 11;

FIG. 3 is a horizontal sectional view, somewhat diagrammatic in nature, illustrating the two interrupting assemblages disposed in an oil circuit-breaker tank, with the location illustrated of the resiliently mounted blast-shields of the present invention;

FIG. 4 is a side elevational view of an oil circuitbreaker tank, partially broken away in section, indicating the internal welding of metallic studs to the inner tank wall for the resilient shield mounting;

FIG. 4A is a showing of a single metallic stud welded to the inner tank wall.

FIG. 5 is a fragmentary sectional view taken substantially along the line V-V of FIG. 4;

FIG. 6 is a side-elevational view of one of the two insulating blast-shields; and,

FIG. 7 is a side elevational view of the other type of insulating blast-shield utilized.

DESCRIPTION OF THE PREFERRED EMBODIMENT The use of baffle structures for oil circuit-breaker tanks is, broadly speaking, quite old in the art. Reference may, for example, be made to McCloud U.S. Pat. No. 3,157,769, issued Nov. 17, 1964. Additionally, damping devices for oil circuit-breakers have been used heretofore, such as that shown in Bergstrbm, U.S. Pat. No. 3,118,997, issued Jan. 21, 1964. Mankoff et al. U.S. Pat. No. 2,998,499, issued Aug. 29, 1961, and Rampath U.S. Pat. No. 3,514,562, issued May 26, 1970, illustrate other baffle-type arrangements. Finally, McCloud U.S. Pat. No. 3,335,245, issued Aug. 8, 1967, illustrates a further type of brittle construction.

The present invention, however, uses a plate of strong insulating non-gas-absorptive material, preferably a glass-polyester laminate, for example, mounted on the internal tank walls of an oil circuit-breaker, and centered on the current interrupter vents. In more detail, with reference to FIGS. 1 and 2 of the drawings, it will be observed that there is illustrated a metal grounded oil tank 1 for accommodating a highvoltage oil-type circuit-interrupter 2. The details of the interrupting structure are not pertinent to the present inven tion, and reference may be made to U.S. Pat. No. 2,816,991, issued Dec. 17, 1957 to Robert E. Friedrich, and assigned to the assignee of the instant application. Generally, as well known by those skilled in the art, during current interruption, pressure is generated internally within interrupting tubes 3 of an extinguishing assemblage 4, and blasted outwardly, as indicated by the arrows 5, illustrated in FIG. 1,-into the general interior 6 of the oiltank body' The present invention is particularly concerned with resiliently absorbing the shock forces exerted during such lateral blasting out of the individual interrupting units, designated by the reference number 3 in FIG. 1.

FIG. 2 illustrates, to a considerably enlarged scale, the welding of metallic studs 8 to the inner tank wall 1 for mounting of the shields l0, 12 of the present invention. It will be observed that molded bumpers 14 of an elastomeric material, such as an oil-resistant rubber, are utilized in conjunction with a molded adapter, designated by the reference numeral 16 in FIG. 2. Preferably, the elastomeric or resilient bumpers 14 are fabricated, for example, of BUNA-N, which is a copolymer of butadiene and acrylonitrile, and is desirably of an insulating electrical grade, with, accordingly, minimum amounts of lamp black or carbon incorporated therein. A possible supplier is the Industrial Rubber Company of Pittsburgh, Pennsylvania. As shown, the molded adapter 16 may have a metallic sleeve 18 of metallic material molded therein, the said sleeve being' internally threaded, as at 18a, to thread over the welded stud 8, which is externally threaded.

It will be observed that the mounting assemblies, generally designated by the reference numeral 20, resiliently mount blast-shields, designated by the reference numerals and 12, and shown in more detail in FIGS. 6 and 7 of the drawings. With reference to FIGS. 6 and 7 of the drawings, it will be observed that each of the blast-shields 10, 12 are provided with four slots 22 to accommodate the inwardly-directed welded studs 8.

Any suitable insulating material could be utilized for the fabrication of the blast-shields 10, 12, but we prefer to utilize blast-shields comprising 0.25 inch thick plates of glass-reinforced polyester laminate. The glass laminate is mounted against molded BUNA-N" rubber bumpers 14 of 70 durometer hardness, which are oilresistant and electrical insulators. These bumpers are placed over the four 0.5 inch threaded studs 8, 2.25 inches long, which have been welded to the inner tank walls 1 of the oil circuit-breakers 2 on, for example, 29 inch centers. A hexagonal steel lock-nut 24 and steel washer 26 placed on the'0.5 inch stud 8, provide dimensional adjustment and a firm backing for the bumper 14. The glass-polyester plate 12 is slotted, as at 22, to permit deflection, as required, to assist in absorbing the shock forces during theopening operation of the circuit-interrupter 2. The mounting is secured with a molded glass-reinforced insulating adapter 16. A threaded steel insert 18, with a rounded head 18b, is used in the molded insulating adapter 16 to provide tensile strength, and to provide a uniform electric potential gradient.

Glass-polyester washers 30 are used on both sides of the 0.25 inch polyester laminate sheet 12 to prohibit access to the slot 22 by the rubber bumper l4 and the neoprene washer 34. The neoprene washer 34 provides a resilient cushion to the reaction forces of the deflection of the polyester laminate 12, and gives a visible indication of torque applied to the molded insulating adapter 16. A total of four blast-shields 10, 12 are mounted in one phase of a three-phase breaker 2, or 12 assemblies 40 are required per 3-pole breaker 2. These are mounted to be centered on the interrupter side blocks, or individual interrupter units 3.

The blast-shields 12, mounted toward the rear (manway) side of the tank 1, have a 12-inch by 14-inch triangular bevel 50 to permit easy access through the manway 52 by maintenance personnel. The blast-shield 12 is of lightweight design, and can easily be modified to permit installation in various designs of circuitbreakers. We have found that a desirable approximate distance from the blast shield 10, or 12 to the tank wall 1 at the center of the blast shield 10 or 12 is 4.06 inches, as indicated at D in FIGS. 1 and 3.

The results of tests performed in the high-power laboratory clearly demonstrates that the oil circuitbreakers cannot interrupt currents above 30,000 amperes asymmetrical percent of rating) with a lineto-ground bias voltage of I98 KV applied, without the possibility of internal insulation breakdown. However, with the installation of the resiliently mounted barriers l0, 12, successful tests were achieved at currents up to 54,000 amperes asymmetrical (22 percent above rating), with a 198 KV bias voltage applied.

It is to be clearly understood that the blast-shields could be fabricated of similar plastic, glass-reinforced, fiberglass polyester, and epoxy materials with equivalent results, as well as variations being possible of the molded rubber bumper 14 to give an acceptable cushioning effect.

From the foregoing description, it will be apparent that there has been provided an improved resiliently mounted blast-shield 10 or 12 located internally within the oil circuit-breaker tanks 1 to resiliently absorb the shock of ionized gas products striking the one or more shields 10, 12 during fault-current interruption. The barrier 10 or 12 is permitted to move to accommodate short-duration pressure differences on the front and rear faces thereof, thus avoiding damaging deflection. The use of the resilient blast-shield 10 or 12 affords a significant increase in the dynamic insulation-withstand strength of the oil circuit-breaker 2. Also, use of the resilient blast shield permits extension of breaker capability without increasing tank size, thus saving considerable dollars.

Although there has been illustrated and described a specific structure, it is to be clearly understood that the same was merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art, without departing from the spirit and scope of the invention.

We claim:

1. An oil circuit-breaker comprising, in combination, a grounded metallic tank, one or more interrupting assemblages disposed within said tank, at least one resiliently-mounted insulating blast-shield formed of relatively hard, rigid, non-gas absorptive plate material disposed closely adjacent the inner wall of the tank yet spaced therefrom to absorb shock forces emanating from the interrupting assemblage, and said blast-shield being additionally located substantially parallel to the tank side wall and interposed between said one interrupting assemblage and the tank side wall.

2. The combination of claim 1, wherein two such resiliently mounted blast-shields are provided diametrically opposite, on opposite sides of said interrupting assemblage, to resiliently absorb the shock forces of the ionized gas products striking the blast-shield.

3. The combination of claim 1, wherein the blastshield is formed of a glass-polyester material.

4. The combination of claim 1, wherein threaded metallic studs are welded to the internal tank wall for the blast-shield mounting.

5. An oil-break circuit-interrupter comprising a grounded metallic tank, a pair of interrupting assemblages disposed within the tank, a conducting bridging member for electrically bridging the two interrupting assemblages, each interrupting assemblage comprising one or more laterally-vented interrupting units having laterally directed vent-openings therein, and each interrupting assemblage having laterally spaced therefrom a pair of resiliently mounted blast-shields formed of relatively hard, rigid, non-gas-absorptive plate material disposed closely adjacent the inner wall of the tank yet spaced therefiom to absorb shock forces emanating from the interrupting assemblages during heavy faultcurrent interruption, and said blast-shields being additionally located substantially parallel to the inner tank wall and interposed between said interrupting assemblages and the tank side wall.

6. A resiliently mounted blast-shield for an oil circuitbreaker tank comprising a generally rectangular insulating plate, stud-means fixedly secured to the inner wall of the tank and protruding through slots provided in said blast-shield, and an elastomeric bumper encircling the stud and resiliently supporting the blastshield.

7. The combination according to claim 6, wherein the insulating shield is of a glass-polyester laminate material.

8. An oil circuit-breaker comprising, in combination, a grounded metallic tank, one or more interrupting assemblages disposed within said tank, at least one resiliently-mounted insulating blast-shield disposed closely adjacent the inner wall of the tank to absorb shock forces emanating from the interrupting assemblage, and elastomeric bumpers being interposed between the tank wall and the blast-shield.

9. The combination according to claim 8, wherein insulating washers encircle the studs on opposite sides of the blastshield for resiliently mounting the same, and preventing the elastomeric bumper from protruding through the slot in the blast shield. l= 

1. An oil circuit-breaker comprising, in combination, a grounded metallic tank, one or more interrupting assemblages disposed within said tank, at least one resiliently-mounted insulating blast-shield formed of relatively hard, rigid, non-gas absorptive plate material disposed closely adjacent the inner wall of the tank yet spaced therefrom to absorb shock forces emanating from the interrupting assemblage, and said blast-shield being additionally located substantially parallel to the tank side wall and interposed between said one interrupting assemblage and the tank side wall.
 2. The combination of claim 1, wherein two such resiliently mounted blast-shields are provided diametrically opposite, on opposite sides of said interrupting assemblage, to resiliently absorb the shock forces of the ionized gas products striking the blast-shield.
 3. The combination of claim 1, wherein the blast-shield is formed of a glass-polyester material.
 4. The combination of claim 1, wherein threaded metallic studs are welded to the internal tank wall for the blast-shield mounting.
 5. An oil-break circuit-interrupter comprising a grounded metallic tank, a pair of interrupting assemblages disposed within the tank, a conducting bridging member for electrically bridging the two interrupting assemblages, each interrupting assemblage comprising one or more laterally-vented interrupting units having laterally directed vent-openings therein, and each interrupting assemblage having laterally spaced therefrom a pair of resiliently mounted blast-shields formed of relatively hard, rigid, non-gas-absorptive plate material disposed closely adjacent the inner wall of the tank yet spaced therefrom to absorb shock forces emanating from the interrupting assemblages during heavy fault-current interruption, and said blast-shields being additionally located substantially parallel to the inner tank wall and interposed between said interrupting assemblages and the tank side wall.
 6. A resiliently mounted blast-shield for an oil circuit-breaker tank comprising a generally rectangular insulating plate, stud-means fixedly secured to the inner wall of the tank and protruding through slots provided in said blast-shield, and an elastomeric bumper encircling the stud and resiliently supporting the bLast-shield.
 7. The combination according to claim 6, wherein the insulating shield is of a glass-polyester laminate material.
 8. An oil circuit-breaker comprising, in combination, a grounded metallic tank, one or more interrupting assemblages disposed within said tank, at least one resiliently-mounted insulating blast-shield disposed closely adjacent the inner wall of the tank to absorb shock forces emanating from the interrupting assemblage, and elastomeric bumpers being interposed between the tank wall and the blast-shield.
 9. The combination according to claim 8, wherein insulating washers encircle the studs on opposite sides of the blast-shield for resiliently mounting the same, and preventing the elastomeric bumper from protruding through the slot in the blast shield. 